1. Field of Invention
This invention relates to an apparatus for curing solvent-free inks, coatings and the like, and it is particularly related to an improved cooling means used therein. More specifically, the present invention is concerned with the utilization of heat pipes for effective cooling in such curing apparatus.
2. Prior Art
As described in U.S. Pat. No. 3,745,307 which was granted to Sandford C. Peek, Jr., on July 10, 1953, solvent-free inks and coatings have recently found increasing industrial utilization in view of the air pollution problems associated with the use of solvent-bearing materials. Curing of such solvent-free inks, coatings and the like is effected by radiation in the ultraviolet and electron beam frequencies, and the curing operation is marked by absence of solvent evaporation and atmospheric pollution.
Basically, the operation described in the aforesaid patent comprises passing a sheet or a web of a printed material below a series of ultraviolet lamps, each lamp being encased within a reflector adapted to direct the radiation toward the moving work. A series of ultraviolet lamps with their associated reflectors, and a varying speed moving work provide for photopolymerization or curing of the solvent-free ink or coating. In order to avoid formation of hot spots in, or overheating of the printed material, each reflector is provided with a shutter means which closes in response to a signal, thus blocking the radiation and preventing it from impinging upon the moving work in order to avoid damage thereto which may otherwise result from excessive or prolonged exposure. Overheating of the ultraviolet lamps, the reflectors and the shutter means is prevented by forced-air cooling of these elements.
Air cooling of ultraviolet lamps, the reflectors and the shutter means in such curing apparatus is but one of the two principal means heretofore employed in the prior art for cooling these elements, while water cooling constitutes the other. However, both air cooling and water cooling have inherent disadvantages. When using air, for example, the rate of heat transfer is inherently low, thus requiring large volumes of air for effective cooling particularly in large scale installations. Additionally, excessive air currents around the lamps' main envelopes cause condensation of mercury and extinguishes the lamps, thus necessitating delay in start up and causing a shortened lamp life.
The main disadvantage of water cooling is from safety standpoint. Since the ultraviolet lamps usually operate at high voltage (approximately 1600 volts) and about 7 amperes, water around the lamps presents the danger of causing a lethal situation to the operating personnel in case of a leak. Accordingly, extreme precautions must be taken to avoid creating such hazzardous conditions.